Diaphragm pumps are particularly useful in the pumping of liquids, although some uses are known for the pumping of gases with a diaphragm pump. Conventionally diaphragm pumps utilize a circular shaped rigid diaphragm with an elastomeric annularly disposed flexible portion at the outer perimeter. The plate is then reciprocated within a pumping chamber by means of either a direct connected mechanical device or an intervening second fluid on the power side of the diaphragm. The circular plate of the conventional diaphragm pump occupies the majority of the aperture opening of the pumping chamber of the pump. In this way the elastomeric perimeter of the diaphragm becomes heavily flexed during the reciprocating action of the diaphragm within the chamber. Since the flexure of the diaphragm is limited to the elastomeric perimeter, considerable wear and early fatigue failure of the elastomeric portion of the diaphragm commonly occurs. Additionally such a conventional diaphragm in conjunction with check valves at the inlet and outlet ports to the pumping chamber results in an essentially positive displacement type of pump. Of course this is not a true positive displacement pump since the existence of downstream back pressure may only reach a certain value before the pump simply stalls and vibrates without pumping fluid. An additional drawback to such a diaphragm pump is that it is difficult to vary the stroke length of the reciprocating diaphragm into and out of the pumping chamber since all flexure takes place in the perimeter and not in the more rigid central portion of the diaphragm.
Therefore, there is a need for an improved diaphragm pump in which the elastomeric portion of the diaphragm does not have such a high concentration of flexure stresses, and additionally there is a need for an improved diaphragm pump which acts more like a positive displacement pump of the piston variety.